This invention relates to surface acoustic wave delay lines.
The propagation of surface acoustic waves between input and output transducers located on the same surface of a body of piezoelectric material is known and has been utilized to fabricate, inter alia, delay lines for radio frequency signals. A common form of delay line is one in which the acoustic waves are propagated in straight lines between transducers located on a flat surface. It is apparent that the maximum delay of such a line is a function of the available length of the flat surface.
In British Pat. No. 1,197,860 there is disclosed a delay line having a single input/output transducer positioned on an annular surface whereby bidirectional acoustic waves launched by the transducer travel around the annular surface and are recovered, in phase, at the transducer to provide the output signal. Typically, the annular propagation path may be on the surface of a cylinder of piezoelectric material.